1. Field
The present disclosure pertains to the field of location systems. More particularly, the present disclosure pertains to techniques for providing improved precision location information using a network based local area augmentation system.
2. Description of Related Art
Mobile communication technologies have recently enjoyed substantial growth and are likely to continue to experience increasing growth and acceptance in the near future. Currently, many cars, trucks, airplanes, boats, and other vehicles are equipped with devices that allow convenient and reliable mobile communication through a network of satellite-based or land-based transceivers. Advances in this technology have also led to widespread use of hand-held, portable mobile communications devices.
Many customers of mobile communications systems also find desirable an accurate determination of their location. Such information may be reported to a remote location to provide various location-based services. For example, a cellular telephone in a vehicle or carried by a person offers a convenient communication link to report location information. Services such as directions or the location of nearby facilities of a desired type may be provided based on the location information relayed. In current systems, location information is generated by traditional positioning systems, including a satellite-based positioning system such as the global positioning system (GPS) using NAVSTAR satellites, the Russian GLONASS system, or the European EUTELSAT system, or a land-based positioning system, such as LORAN-C. These approaches, however, may not be suitable for particular applications that require highly accurate and/or reliable location information.
One known technique for providing improved location information involves the use of differential GPS calculations (see, e.g., U.S. Pat. No. 5,913,170). Such systems may use a single fixed base station in a known location with a GPS receiver to generate correction signals. These correction signals are relayed to the mobile device (e.g., a phone), where they can be used to improve the accuracy of the location information derived by a GPS receiver in the phone. The use of a single base-station based correction information computation engine and a single tower's GPS receiver to perform calculations may be convenient; however, the accuracy and reliability of such systems may still not be sufficient for applications that benefit from highly precise location information.
Some other prior art systems utilize various fields of antennas or receivers to generate correction information. For example, a local area augmentation system (LAAS), also known as a ground based augmentation system (GBAS), may be used in airplane navigation and landing systems (see, e.g., U.S. Pat. No. 6,067,484). Such systems employ multiple ground receivers or beacons in fixed locations aligned along a runway. These receivers each individually transmit correction information to the GPS receiver in the airplane, which performs computations including all the information from the multiple receivers. This type of arrangement may be impractical for cellular phone and other consumer-oriented location devices because additional radio frequency receivers are needed to receive information from the runway beacons and because the multiple beacons each provide data requiring substantial additional computations at the GPS receiver. Such complicated processing may disadvantageously burden the processing resources and/or the power (e.g., battery) resources of a mobile device. Moreover, wide deployment of many such beacons solely for the purpose of a positioning system would be a costly undertaking.
Additionally, one other prior art location technique is a wide area augmentation system (WAAS). The WAAS also provides supplemental correction data in order to establish better locations. One such system is being deployed with a limited set of antenna stations (currently 25) being deployed throughout the United States. This system, however, also relies on radio-frequency transmission of correction information. Moreover, correction data from single, widely spaced antennas may not provide sufficiently accurate correction information to allow sufficiently precise location calculations to be performed for some applications.